import turtle
turtle.shape("turtle")
turtle.hideturtle()


def goto(x, y):
    turtle.up()
    turtle.goto(x, y)
    turtle.down()

Y = 320


def d_dot():
    turtle.clear()
    global Y
    goto(0, Y)
    turtle.dot(50, "green")
    Y-=5
    turtle.ontimer(d_dot,50)

turtle.tracer(False)

d_dot()
turtle.done()

